1. Field of the Invention
Applicant's invention is used with a molten material to form an electrolyte cell. Such a cell is sometimes referred to as a galvanic cell or an electrochemical concentration cell. Devices of the foregoing type are variously classified in the United States Patent Office in official subclasses entitled, "Batteries, Electrolytes; or Chemistry, Electrical and Wave Energy, Processes and Products, Electrolysis, Analysis and Testing; or Chemistry, Electrical and Wave Energy, Apparatus, Electrolytic, Analysis and Testing, Solid Electrolyte; or Electricity, Measuring and Testing; Determining Non-Electrical Properties by Measuring Electrical Properties."
2. Description of the Prior Art
During the past several years considerable time and money has been expended by many individuals in an effort quickly to determine and/or control the amount of one or more constituents in a bath of molten material by means of techniques utilizing a galvanic cell, i.e., an electrolytic cell. Much has been accomplished towards the development of electrode assemblies suitable for insertion into a bath of molten metal such as liquid aluminum, copper, iron, or steel to form therewith an electrolytic cell for determination of the concentration of a constituent, frequently oxygen. The state of the art as of 1968 and a brief historical review of developments relating to oxygen determination is set forth in a paper prepared for presentation at the 76th General Meeting of American Iron and Steel Institute, in New York, May 23, 1968, by E. T. Turkdogan and R. E. Fruehan entitled "Rapid Oxygen Determination in Liquid Steel." A copy of the paper is available upon request from the American Iron and Steel Institute, 150 E. 42nd Street, New York, New York 10017.
In the Turkdogan et al. paper there is disclosed a disposable immersion type, plug-in unit including a reference electrode assembly for forming an electrolytic cell when immersed in liquid steel. The plug-in electrical connections are like those used in disposable, i.e., expendable immersion thermocouples of the plug-in type disclosed in U.S. Pat. Nos. 2,999,121--H. G. Mead; 3,024,295--P. J. Moore; and 3,048,642--K. B. Parker, Jr. Expendable thermocouples are well known to those skilled in the arts wherein the temperature of a bath of molten material is to be measured and particularly to those skilled in the arts of producing steel and cast iron. Thermocouples of this type are plugged into a receptacle at the immersion end of a manipulator, sometimes referred to as a holder or a lance, which established an electrical connection to a measuring circuit which generally includes a self-balancing potentiometer recorder.
U.S. Pat. No. 3,785,947--W. H. Baldwin et al. also discloses a plug-in immersion assembly which when immersed in a molten metal forms an electrolytic cell for measuring oxygen in a bath of molten steel.
In the processing of steel a plug-in unit including structure for immersion in a molten bath to form an electrolytic cell for the determination of oxygen as disclosed in the Turkdogan et al article and the Baldwin et al. patent has been found very convenient to use. A similar construction for obtaining a measure of other constituents in steel or other molten materials would likewise have great utility, however, when the temperature of the molten material is high relative to the melting temperature of constituent-responsive electrolyte materials such, for example, as for the determination of manganese in molten steel, it has heretofore been considered impossible to make a structure suitable for insertion in the bath of molten material to form therewith an electrolytic cell.
The principles of electrochemical cells are well known to those skilled in the art and are set forth in greater detail in text books, the Turkdogan et al. paper, and the references listed in the bibliography thereof. Since the principles per se are not applicant's invention they will be treated only briefly herein.
An electrochemical cell may be schematically represented generically in a table as follows:
Table I __________________________________________________________________________ 1 2 3 4 (A) .vertline. (B) .vertline. (C) .vertline. (D) .vertline. (F) Electronic Molten Constituent Reference Electronic conductor sample responsive potential conductor containing material producing constituent i.e. material to be Electrolyte measured Material __________________________________________________________________________
In the above representation the substances comprising the cell are symbolized by letters. The numbered vertical lines represent phase boundaries and hence sources of e.m.f. For sake of simplicity the electronic conductors A and F are assumed to be solids. The molten sample B is assumed to be liquid. The reference potential producing material D depending upon the constituent to be measured, may be a solid, liquid, or gas. The constituent-responsive material, i..e., electrolyte material C may be either a solid or liquid and will be chosen for its ability to develop a thermodynamically reversible e.m.f., i.e., an interfacial voltage with respect to the activity (concentration) of the constituent of interest at either interface or phase boundary 2 or 3. Solid or liquid conditions other than those assumed if kept constant will not change the basic theory as presented. Constancy, or approximate constancy, of temperature of the cell is assumed in considering the e.m.f.'s at the interfaces 1 through 4.
As disclosed in an article entitled "On the Activities of Coexisting Elements in Molten Iron. III The Activity of Mn in Molten Fe-Mn Alloy" by Koji Sanbongi and Masayasu Ohtani, Science Reports of the Research Institute, Tohoku Univ., Sendai, Series A, Vol. 7 pp. 204-209 (1955) the Mn content in iron has been measured using an electrolytic concentration cell wherein the components corresponding to B, C, and D of the above table comprised liquids contained in a crucible of special shape. The cell is represented by the following table:
TABLE II ______________________________________ 1 2 3 4 (A) .vertline. (B) .vertline. (C) .vertline. (D) .vertline. (F) W .sym.Fe--Mn SiO--MnO-- Mn.crclbar. W MgO--CaO ______________________________________
That is to say molten Mn was used as the standard electrode to provide a reference potential, molten Fe--Mn alloys containing various amounts of Mn constituted the other electrode and molten slag containing MnO was used as the intermediate electrolyte. A special crucible containing the molten materials was made of MgO and the synthetic slag was obtained by melting high purity MnO, SiO.sub.2, and CaO in an MgO or Al.sub.2 O.sub.3 crucible and pouring it into the special crucible. Tungsten wires having ends extending into the molten Fe--Mn alloy and the molten Mn provided electrical connections for the cell and the e.m.f. between them was measured with a potentiometer.
While the cell above described is satisfactory for the measurement of Mn in Fe--Mn alloys it would appear to be limited in its use to laboratory type operations. There is no apparent way of employing it for insertion into a bath of molten material such as that contained within a furnace or ladle in the manner described by Turkdogan et al.
While theoretically any of many presumably stable manganese compounds such as MnO, Mn.sub.2 P.sub.2 O.sub.7 ; Mn.sub.2 SiO.sub.4 ; and MnSiO.sub.3 ; for example, would appear to be suitable materials to develop a potentiometric signal, that is, a thermodynamically reversible e.m.f. with respect to the manganese activity (concentration) at either interface, i.e., phase boundary 2 or 3, it has not heretofore been known how to employ such materials in a structure which can be immersed in a bath of molten metal at temperatures as high as the temperature of molten steel.
Applicant has discovered a way whereby it becomes possible to utilize in an assembly for insertion in a bath of molten material constituent-responsive materials which are ionically conductive and/or may melt or soften at a temperature below the operating temperature of an electrolytic cell.